This invention relates to a pneumatic tire having an integrated circuit transponder located within the structure of the tire for use in tire identification and/or other data transmission. More particularly, the invention relates to the combination of a pneumatic tire and a transponder of the type using an electrical coil as its antenna. The transponder is a passive device in that it has no source of electrical energy but instead depends upon the receipt of an "interrogation" signal emanating from a source outside of the tire. The interrogation signal is rectified by the circuitry in the integrated circuit transponder, which then utilizes the rectified signal as a source of electrical energy for use in its transmission of an electrical signal digitally encoded to identify the tire. A unique code can be used for each tire.
Reference is made to commonly-assigned U.S. Pat. No. 4,911,217 issued Mar. 27, 1990, to Dunn et al. which discloses a commercially-available integrated circuit transponder suitable for use in a pneumatic tire and which discloses an electric-field coupled interrogator/transponder system. The disclosure of U.S. Pat. No. 4,911,217 is incorporated herein by reference and is referred to below as the Dunn et al. patent.
An alternative integrated circuit is commercially available from Texas Instruments of Austin, Tex., and is sold under the name TIRIS.TM., for Texas Instruments Registration and Identification System. While these integrated circuits are not ideal, they are preferred because of their commercial availability. The integrated circuit disclosed in U.S. Pat. No. 4,911,217 also is preferred because it is the only integrated circuit that has been successfully tested in the subject invention.
In the manufacture of pneumatic tires, it is desirable to provide unique numerical identification for each tire as soon as possible during the course of its fabrication. Also, the identification should be easily discernible throughout both the manufacturing process and the life of the tire, and retreading of the tire should not adversely affect identification. If the tire is mounted on a steel or aluminum wheel, as is the normal case, or on a dual wheel assembly, then the tire identification should still be easily acquired by tire owners and users for use in inventory control, record keeping and warranty determination. The ability to identify tires throughout their manufacture is particularly valuable in quality control because the source of manufacturing problems can be much more readily ascertained than is the case in the absence of specific tire identification. Statistical process control and other methods can be used with tire identification to detect process parameters that are going out of control or to detect machinery wear, failure, or maladjustment. These benefits of tire identification practically speaking cannot be obtained unless a radio-frequency transponder is available for incorporation in a tire. The transponder must be quite inexpensive, reliable, and readable from any position around the tire or vehicle wheel on which it is mounted; it also must survive manufacturing processes, be usable during the course of manufacture and must not adversely affect tire life or retreadability.
Unfortunately, the Dunn et al. system of electric field coupling has been found inadequate for use in steel-reinforced truck tires because of the power and other restrictions applicable to tire identification. The Federal Communications Commission, for example, in Part 15 of the FCC Regulations applicable to low power communications devices, specifies radiation limits as a function of frequency. This is done in a step fashion, such that the greatest field strength is permitted in the frequency range from 9 KHz to 490 KHz. In this frequency range, the measurement distance for field strength from the source of the radiation is 300 meters and the field strength, in microvolts per meter, must be less than 2400 divided by the frequency F in KHz. At frequencies from 490 KHz to 1705 KHz, the field strength can be 10 times as great, i.e., 24,000 microvolts per meter divided by the frequency in KHz, but the measurement distance is only 30 meters instead of 300. This means that the permitted transmitter power levels are considerably less at these higher frequencies because field strength is inversely related to the square of the distance from the source (the cube of the distance for near-field effects). This dictates the use of the lower frequencies in tire identification applications.
It was stated above that it is desirable in a tire application to be able to read the transponder identification and data information from any position around the circumference of the tire. The Texas Instruments' TIRIS.TM. and Destron/IDI integrated circuits, the latter of which is described in Dunn et al., were designed primarily for use in animal identification. In animal identification applications, the integrated circuits are attached to a small electrical coil having a ferrite core within it, and a capacitor may be connected in parallel with the coil as well if it does not have enough parasitic capacitance for tuning of the parallel circuit to the frequency of the interrogation signal used to activate the transponder. The aspect ratios of the coil and ferrite core are very low in that the coil diameter is much smaller than its axial length. These components typically are enclosed within a glass or plastic tube that is sealed at the ends. The capsule formed in this manner then can be injected into an animal for permanent animal identification.
One of the inventors in 1986 placed one of these miniature animal-identification transponders into a pneumatic tire for preliminary evaluation. The integrated circuit was of the type described in the Dunn et al. patent, but the Texas Instruments TIRIS.TM. device for animal identification now also has been placed in tires for evaluation. These devices, while being placed parallel with the wires in the bead bundle of the tire and near it, have had the disadvantage that interrogation and identification could only be achieved in the area of the tire near the location of the transponder, that is, the transponder could not be interrogated from any position around the tire. Another disadvantage of these very small devices is that their ferrite cores provide greater frequency selectivity than is desirable for a high volume, inexpensive transponder intended for industrial and commercial use. While the high selectivity or "Q" of a ferrite-coil-tuned circuit is desirable in many radio frequency applications, transponder applications require that a single reader be capable of reading many transponders, which, if selective in frequency, must be precisely tuned so that all can be read with the same precisely tuned interrogation signal.
Several years ago, Identification Devices, Inc. of Boulder, Colo., discussed tire identification applications of transponders with several of the present inventors. As a result of these discussions and perhaps others, Identification Devices became aware of the desirability of being able to read a transponder from any location around the tire. Subsequently, Destron/IDI (a legal entity that purchased assets of Identification Devices) proposed the vehicle tire identification system described in the international application published under the Patent Cooperation Treaty as Publication No. WO90/12474 dated Oct. 18, 1990 (hereinafter referred to as the PCT publication).
In essence, the invention disclosed in the PCT publication involves a transponder coil having one or more conductive turns as an antenna, the lead wires of which must be electrically connected to the integrated circuit of a transponder. The antenna is positioned in a vehicle tire having sidewall and tread surfaces. The antenna coil and the integrated circuit are positioned "internally to said tire with said coil positioned with the loop thereof in a relatively constant relationship relative to one of said tire surfaces" (amended claim 1 of the PCT publication). This, in effect, means that the coil in the disclosed system must be, as illustrated, larger than the bead diameter of the tire, circular in shape, and coaxial with the tire's axis of rotation.
Several of the inventors witnessed a demonstration by Destron/IDI of its device, which included a coil and transponder attached to its ends. The coil and transponder were temporarily attached to the innerliner of an unmounted pneumatic truck tire. The transponder in this demonstration tire could be read from any location around the tire with the interrogation signal provided by the Destron/IDI reader. This demonstration took place in April of 1989, a date subsequent to the Mar. 31, 1989 priority date indicated in the PCT publication.
The inventors do not regard the apparatus described in the PCT application as being suitable for pneumatic tire use because, as taught by the inventors in the PCT publication, the coil must be located away from the bead area of the pneumatic tire, such as in the tread area or upper sidewall, and because the integrated circuit must be electrically connected to the ends of the large-diameter antenna coil in these high-deformation areas of the tire.
A pneumatic tire is a laminated article which begins with a cylindrical shape approximately equal in diameter to that of the tire's bead diameter. During manufacture, the beads are brought axially toward one another and the center portion of the tire increases in diameter as the tire takes on its toroidal shape. After this diameter increases, the restrictive belt plies, at least in radial ply tires, are added, as is the circumferential tread rubber. Insertion of an antenna of the type described in the PCT publication in a laminated pneumatic tire, with the integrated circuit connected between the coil ends, would have to be accomplished after the tire had taken on its toroidal shape and would have to accommodate the further expansion of the toroidal shape when the tire is forced radially outwardly into the mold cavity. This would require the capability of elongation in the conductive material forming the antenna coil, and the integrated circuit connections to the coil would be required to withstand tensile stress. Also, a transponder of this design would not be expected to be durable in normal tire use because of its required positioning in the upper sidewall or tread areas of the tire.